The present invention relates to a process to form a polyamide composition comprising a blend of polycaprolactam and poly(hexamethylene adipamide); more particularly, the invention relates to a process to form a film from such a composition.
Films made of polyamides, including polycaprolactam (nylon 6) and poly(hexamethylene adipamide) (nylon 6, 6), are well known. Polycaprolactam and poly(hexamethylene adipamide) films have similar properties as might be expected from their common polyamide family background. There are distinguishing characteristics between polycaprolactam and poly(hexamethylene adipamide). Generally, polycaprolactam is a tougher, more flexible polymer than poly(hexamethylene adipamide). When formed into film, these properties result in a tougher, more flexible film. Poly(hexamethylene adipamide) results in a stiffer film having slightly higher tensile properties.
In addition to these above-noted differences in physical properties, a common difference in properties between polycaprolactam and poly(hexamethylene adipamide) is their melting points. Polycaprolactam typically melts at a temperature of 215.degree. C. to 225.degree. C. (419.degree. F. to 437.degree. F.). While poly(hexamethylene adipamide) melts at a temperature range of about 240.degree. C. to 265.degree. C. (464.degree. F. to 509.degree. F.). These differences in melting temperature are important in the areas of melting to process the polymer as well as indicating the differences in use temperature of the polymers. The differences in melt temperature are particularly important in considering forming films using blown film processing.
When forming films using blown film processing, a tube is extruded and inflated with air. A bubble forms immediately after the extruder die. The maintenance of the desired bubble configuration is sensitive to temperature. It is desirable to maintain the temperature of the film passing through the bubble as low as possible so that the film is relatively stiff and the bubble will not collapse. It is also desirable to maintain the film temperature low so that the bubble can be collapsed without the inner walls of the bubble sticking together. The lower the temperature of the film passing through the bubble, the faster the bubble can be collapsed and the film passed to the next processing step.